Error should be fixed soon.
A team of monkeys was dispatched to fix an issue with YouTube's server, the company revealed in their "500 Internal Server Error" page.
Apparently, the monkeys are going to fix the server with a hammer, as seen in this screenshot of that error page:
Here's a text version of that error if that image isn't showing up for you:
500 Internal Server Error
Sorry, something went wrong.
A team of highly trained monkeys has been dispatched to deal with this situation.
If you see them, send them this information as text (screenshots frighten them):